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Choobus wrote
Energy and momentum do not imply rest mass. Photons move at the speed of light, and it is impossible for anything with mass to move at the the speed of light, but at the same time it is clear that photons have energy. It is the rest mass you have to consider.
The proper time (tp) experienced by any observer depends on their speed. In SR it is tp = INT [sqrt{1-(g^2)}] dt, where g = v/c. Clearly if v = c, g = 0 and tp = 0 as well. (see here for more details). Photons do NOT age. There are no slow photons. When people talk about slowing light down they don't slow down an actual photon, they put light into a BEC or a "photonic" crystal or something and the group velocity is reduced . It's in no way a violation of SR. |
OK, gotcha, thanks for your patient and illuminating explanations.
BTW, if g = v/c and v = c, isn't g = 1?